Managing Patient-Ventilator Asynchrony

Initial Detection and Assessment

Waveform analysis is essential for patient-ventilator asynchrony, requiring careful examination of pressure and flow waveforms, and the most sensitive detection method involves simultaneous recordings of diaphragm electrical activity and esophageal pressure changes, though this is not routinely available 1
Ineffective triggering, often due to intrinsic PEEP, can be identified through waveform analysis, where patient inspiratory efforts fail to trigger the ventilator 1
Delayed triggering, a lag between patient effort and ventilator response, can be detected through waveform analysis 2

The American Thoracic Society recommends using flow triggers instead of pressure triggers, as they reduce the incidence of asynchrony 1
Flow sensors detect changes in machine-produced bias flow and generally provide better patient comfort 2
Setting EPAP/PEEP to offset intrinsic PEEP (typically 3-5 cm H₂O) reduces the effort required to trigger a breath and improves patient comfort in patients with COPD or airflow obstruction 1, 2
Setting PEEP greater than intrinsic PEEP can be harmful and worsen hyperinflation 1, 3
Intrinsic PEEP in severe COPD may reach 10-15 cm H₂O, but EPAP levels >5 cm H₂O are rarely tolerated 2
Prolonging expiratory time reduces dynamic hyperinflation and gas-trapping 1
Inadequate pressure support causes increased respiratory rate and patient distress, and titrating pressure support upward while monitoring patient comfort and respiratory rate is recommended 1
Avoiding excessive pressure support, which can cause hyperventilation during sleep, central apneas, and worsen asynchrony, is crucial 4, 5
Switching to timed/assist-control mode for patients with advanced respiratory failure, neuromuscular disease, or dependence on hypoxic respiratory drive may be necessary 2
Considering proportional modes (PAV or NAVA) can reduce asynchrony and improve sleep quality, but has not yet demonstrated improved clinical outcomes regarding duration of mechanical ventilation or mortality 4, 5

In obstructive lung disease (COPD, Asthma), prioritizing prolonged expiratory time, using modest PEEP (3-5 cm H₂O) to offset iPEEP, and never exceeding intrinsic PEEP with applied PEEP is recommended 1, 2
In restrictive disease (neuromuscular, chest wall), achieving adequate tidal volume with relatively low pressures (10-15 cm H₂O) in neuromuscular disease, and higher pressures in chest wall disease due to reduced compliance is necessary 1
In ARDS, using a low tidal volume strategy (6-8 mL/kg ideal body weight) and considering lung recruitment with PEEP for persistent hypoxia is recommended 1, 6

Checking patient comfort and respiratory rate immediately after any ventilator adjustment, and reassessing waveforms continuously to ensure the intervention resolved the specific asynchrony type is crucial 1
If the breathing rate falls after adjusting pressure support, the support was inadequate 1

Excessive oxygen flow rates (>4 L/min) can cause mask leak and delayed triggering, promoting asynchrony 7
Ignoring waveforms can lead to subtle asynchronies being undetectable 1
Treating agitation with sedation first, without ruling out asynchrony as the cause, can worsen patient outcomes 1
Setting PEEP too high in obstructive disease can worsen air trapping rather than helping 1, 3

In severe chronic obstructive pulmonary disease (COPD), intrinsic (auto) PEEP can reach 10–15 cm H₂O, creating a substantial inspiratory threshold load that impairs the patient’s ability to trigger the ventilator. 8
Obstructive lung diseases such as COPD and asthma predispose patients to intrinsic PEEP and dynamic hyperinflation, increasing the likelihood of trigger and cycling asynchrony. 8
In patients with advanced acute respiratory failure, spontaneous effort may cease when the ventilator “captures” the breath, and those who rely on hypoxic drive can exhibit unreliable triggering. 8

Excessively long expiratory times in assist‑control modes generate prolonged “lock‑out” periods that prevent patient‑triggered breaths, a problem that is especially pronounced with the SIMV mode. 8

Setting external PEEP/EPAP to offset intrinsic PEEP—typically 3–5 cm H₂O—reduces the inspiratory threshold load and improves trigger sensitivity; however, EPAP levels above 5 cm H₂O are rarely tolerated when intrinsic PEEP is 10–15 cm H₂O in severe COPD. 8
Using flow‑based trigger settings rather than pressure‑based triggers decreases the incidence of ineffective and delayed triggering and generally enhances patient comfort. 8
Flow sensors that monitor changes in the ventilator’s bias flow provide superior trigger sensitivity and faster ventilator response times compared with pressure triggers. 8

Switching to a timed or assist‑control ventilation mode is recommended for patients with advanced respiratory failure, neuromuscular disease, or dependence on hypoxic respiratory drive, because these patients may be unable to generate sufficient spontaneous effort to trigger breaths. 8
A timed mode is particularly important during sleep for patients whose respiratory drive is insufficient to trigger the ventilator, ensuring reliable breath delivery. 8